An image sensor may be a semiconductor sensor that may transform an optical image to an electrical signal. The image sensor may include an optical sensor part, that may sense light, and a logic circuit part, that may transform sensed light into the electrical signal. The sensed image may thus be transformed into data.
A complementary metal oxide semiconductor (CMOS) image sensor may use a switching method. The switching method may sequentially detect an output using MOS transistors. There may be as many MOS transistors as there are pixels using CMOS technology.
A unit pixel of a CMOS image sensor may include a photodiode as a photo detector and four transistors. The four transistors may include a transfer transistor for transferring a photo-charge focused on the photodiode to a floating node, a reset transistor for resetting the floating node by removing the charge stored in the floating node, a drive transistor for operating as a source follower buffer amplifier, and a selection transistor for performing switching and addressing.
FIG. 1. illustrates a related art image sensor.
Referring to FIG. 1, a field oxide layer 120 may be formed on semiconductor substrate 100, including P− epi layer 110. An NMOS transistor, which may include gate dielectric layer 130, gate 140, and an N+ junction region (not shown), may be formed at one side of substrate 100. A photodiode, for example having a PNP structure with deep N− region 151 as photo detector, P0 region 152, and epi layer 110, may be formed at the other side of substrate 100 adjacent to gate 140. Gate 140 may be a transfer gate.
Interlayer dielectric layer 160 may be formed on substrate 100 and may surround a side portion of gate 140. Interlayer dielectric layer 160 may include first oxide layer 161, second oxide layer 162, and nitride layer 163 that may be sequentially stacked. The photodiode may be exposed by forming an opening 160a in interlayer dielectric layer 160. First oxide layer 161 may be formed of a silicon oxide (SiO2). Second oxide layer 162 may be formed of a TEOS layer. Nitride layer 163 may be formed of a silicon nitride (SixNy).
However, in the related art image sensor, a part of light incident on the photodiode through micro lens 170 and a color filter may be out of the photodiode because of a high refractive index. Therefore, an electron-hole pair generation may be reduced and a performance of the image sensor may be degraded.